The present invention is directed to a method for setting the performance of a gas-operated cooking device as well as to a cooking device that uses the method.
Problems can occur in the operation of a gas-operated cooking device, particularly in mobile employment or given an operating in a gas network, wherein the gas quality changes. On one hand, a different gas quality, particularly a change in the type of gas employed, will lead to a change in the air ratio of a combustion gas/air mixture supplied to a gas burner arranged in the cooking device. The ratio of air quantity to combustion gas quantity referred to the stoichiometry of the combustion gas and a change in the ratio of air quantity to combustion gas quantity causes a deviation in the combustion from a desired ideal value for a hygienic, complete combustion, so that increased emissions of pollutants can occur during the combustion. Both increased emissions of pollutants as well as increasing stresses on the component parts will occur from incorrect settings of air quantity and/or combustion gas quantity. On the other hand, a deviation from the ideal air ratio leads to a modified calorific output or heating capacity of the gas burner, which, given a continuous operation of the gas burner during a cooking process, leads to modifications of the cooking time and, thus, to a deterioration of the quality of the cooked product that is being prepared. A modulating operation of the gas burner, in fact, makes it possible to slightly reduce the influence of variable environmental conditions, which, in addition to gas quality, also includes changes in air or gas pressures and contamination of the cooking device, on the quality of the cooked product without, however, being able to completely eliminate this problem. Given cooking devices known from the prior art, a manual intervention is necessary for actuating components of the gas feed and of the air feed in order to adapt the cooking device for the variable environmental boundary conditions, which are usually not to be implemented technically correct by an untrained user.
Additional various methods for optimizing the combustion of a gas burner in and of itself are known from the prior art. German Patent Document DE 196 39 487 A1 discloses a method and an apparatus for optimizing the operation of a gas burner. Even without utilization of an oxygen sensor in the flue gas exhaust, the air-gas mixture for a gas burner is thereby optimized given employment of combustion gasses with different Wobbe indices in that the gas burner is first supplied with an air-gas mixture with a gas excess, and this is ignited. Subsequently, the air part in the air-gas mixture is increased until the flame lifts off from the gas burner, which is detected via a flame sensor. The air-gas ratio is then modified to decrease the air excess in order to set an optimum combustion. A disadvantage of this method, however, is that the gas consumption is elevated during the setting procedure when the air-gas ratio is set proceeding therefrom that the gas part is reduced proceeding from a high initial value given a constant air feed, which will lead to an increase in the operating costs and deflagration can occur given the ignition of the rich gas to air mixture, which reduces operational safety.
Additional methods or devices are known from the prior art that enable the determination of the Wobbe index and/or of the calorific value of a combustion gas supplied to a gas burner in order to set the air ratio needed for a hygienic combustion with the data acquired therefrom.
German Patent Document DE 41 18 781 A1 discloses a method and apparatus for a combustion-free determination of the Wobbe index and/or of the calorific value of a gas. For determining the Wobbe index, the volume stream of a flowing gas is measured and further characteristic properties, such as pressure drop, density, viscosity or the like are measured or kept constant. With the assistance of approximation functions, the Wobbe index of the combustion gas is subsequently identified from the measured volume stream and, thus, mass stream and at least one further characteristic. It is also proposed that the identified Wobbe index be used in order to set the quantity of the heat supplied to a gas burner by varying the pressure and, thus, the volume stream of the delivered gas or by varying the mixing ratio of the two gas grades. A disadvantage of this method, however, is that it requires an additional measuring instrument, which increases the structural outlay of the gas burner mechanism, the manufacturing costs of the device and also has an increases susceptibility to malfunction.
German Patent Document DE 198 24 523 A1, which discloses a regulating method for gas burners, and German Patent Document DE 39 37 290 A1, which discloses a method and a device for producing a fuel/combustion mixture to be supplied for combustion, disclose that an ionization electrode is arranged in the flame region of the gas burner with the result that an electrical conductivity is measured in this region and the stoichiometry of the supplied fuel can be determined therefrom. The calorific value can then be derived from the identified stoichiometry. A disadvantage of this method, however, is that the measurement method has a high susceptibility to error, since the determination of the conductivity is dependent on the exact known geometry of the electrode arrangement, and deviations from the ideal air ratio when setting the air-gas mixture can occur dependent on an imprecisely measured ionization current.
German Patent Document DE 198 38 361 A1 also discloses that the gas composition of a mixture supplied to a gas burner be identified by a sensor arranged in the gas conduit, particularly in the form of a metal oxide sensor. The gas composition identified in this way is then used for determining the calorific value of the combustion gas and for setting a corresponding Wobbe index for the gas mixture by varying the mixture composition. A disadvantage of this method, however, is that expensive sensors must be employed in order to achieve an adequate measuring precision in the determination of the gas composition, and the determination of the caloric value involves complicated conversions that can be affected by errors. Moreover, additional inserts are provided in the gas burner, which increases the design outlay for the device.
German Patent Document DE 199 08 885 A1 discloses a method for the operation of an energy converter supplied with combustion gasses with varying composition. It is provided in this method that the combustion gas is heated in a lockable measuring chamber, and the dependency between the heat quantity supplied to the measuring chamber and the rise in pressure and/or temperature in the measuring chamber is used in order to set the combustion gas composition to a rated value. A disadvantage of this method, however, is that additional inserts are provided and the measurement method is imprecise and susceptible to disturbance due to the determination of the supplied heat quantity that is sensitive to change in the environmental conditions.
German Patent Document DE 199 21 167 A1 discloses a method and an arrangement for measuring the calorific value and/or the Wobbe index of combustion gasses, particularly natural gas. In this method, the speed of sound or the density of the combustion gas is measured, the combustion gas is exposed to an infrared radiation, the part of the infrared radiation absorbed by the combustion gas is measured, and the calorific value and/or the Wobbe index is obtained from these two measured signals. A disadvantage of this method, however, is that it also is technologically complicated and susceptible to malfunction.
German Patent Document DE 197 50 873 A1 discloses a method for the control of an atmospheric gas burner for heating units, particularly water heaters. In order to adapt the starting gas quantity to various environmental conditions, it is proposed that the starting gas quantity be increased time-dependent during the starting procedure, so that a plurality of ignition attempts are undertaken for each starting gas quantity. The starting procedure is interrupted after a previously-defined plurality of unsuccessful ignition procedures and the heating unit is switched to malfunction. A disadvantage of this method, however, is that a hygienic, for example complete, combustion by the gas burner is not assured.
It is therefore an object of the present invention to offer a method for setting the performance of a gas-operating cooking device that overcomes the disadvantages of the prior art and, in particular, automatically adapts to various environmental conditions.
This method is inventively achieved in that the performance setting occur by setting a complete combustion of a combustion gas/air mixture supplied to a gas burner of a cooking device by the following steps:
determining a calorific output to be output by the gas burner and the air ratio required for a complete combustion;
setting the air quantity supplied to the gas burner dependent on the identified calorific output and the identified air ratio; and
setting the specific air ratio via setting of the combustion gas quantity supplied to the gas burner given a constant feed of the air quantity that has been set, so that the composition of the combustion gas/air mixture lies below the lower ignition limit at the beginning of a first ignition attempt of the mixture, subsequently increasing the delivered combustion gas quantity and again attempting ignition, continuing the steps of increasing the quantity of the combustion gas and ignition attempts until there is a successful ignition, for example up to the ignition point, wherein the quantity of combustion gas supplied at the ignition point of the combustion gas/air mixture is acquired, the calorific value of the combustion gas is determined from the acquired, supplied quantity of the combustion gas, and the combustion gas quantity needed for a complete combustion is set by this derived calorific value.
What is to be understood by determination of the calorific output and of the air ratio is, for example, a selection, defining or the like of these quantities.
It can thereby be provided that the combustion gas feed is interrupted between two successive ignition attempts and the gas burner outlet is rinsed with air. It is also inventively proposed that the specific calorific value is corrected by measuring at least one temperature characteristic for the combustion of the combustion gas/air mixture, preferably the flame temperature, at the ignition point and/or by measuring the change of the first temperature given increases of the delivered gas quantity by at least one first sensor.
It can thereby be provided that the combustion gas feed is interrupted between two successive measurements of the first temperature and the area of the first sensor is flooded with air and is essentially cooled to room temperature.
It is inventively preferred that the identified calorific value is corrected by measuring at least one second temperature characteristic for heating of the cooking device via at least one second sensor.
A development of the inventive method is characterized in that the identified calorific value is corrected by measuring the quality of the combustion of the combustion gas/air mixture via at least one third sensor, like a probe, in the exhaust gas path of the gas burner for acquiring at least one exhaust gas component characteristic for the combustion.
For modifying the calorific output, particularly during operation of the cooking device, it is also proposed with the invention that the quantity of air supplied to the gas burner is adapted, preferably without interrupting the air feed, and that the quantity of combustion gas supplied to the gas burner is adapted dependent on the specific calorific value of the combustion gas for setting the desired air ratio, preferably without interrupting the feed of the combustion gas.
An especially preferred embodiment of the method is characterized in that the specific calorific value is stored and utilized for setting a complete combustion.
It is also proposed with the invention that a re-determination of the calorific value is implemented in certain statuses of the cooking device, preferably after separation of the cooking device from a supply of combustion gas and/or from an energy supply, after upward transgression of a prescribed operating time, after upward transgression of a prescribed off time and/or the like, particularly following a confirmation on the part of a user.
The object directed to the cooking device is achieved in that, for utilizing the inventive method, the cooking device comprises a cooking chamber that is heatable via a gas burner, the gas burner comprises a combustion gas feed with a first valve, an air feed with a blower and/or a second valve, an ignition device and a control and/or regulating device in an interactive connection with the first valve, the second valve, the blower and the ignition device.
An inventive cooking device is also characterized by the first temperature sensor at the output of the gas burner, preferably in the flame region of the gas burner, a second temperature sensor in the cooking chamber and/or an exhaust gas sensor in the exhaust gas path of the gas burner, preferably in the exhaust of the cooking device, so that the first temperature sensor, the second temperature sensor and/or the exhaust gas sensor has or, respectively, have an interactive connection with the control and regulating device.
In an inventive cooking device, finally, at least one first device for recognizing a separation from a combustion gas supply and/or energy supply and/or a second device for determining operating time and/or the off-time of the cooking device can be provided in an interactive connection with the control and/or regulating device.
The invention is based on the surprising perception that a method for setting the performance of a gas-operated cooking device can be implemented so that the cooking process can be reproducibly implemented in the cooking device independently of variable environmental conditions, such as change in the gas quality, changes in the air or gas pressure or contamination of the cooking device. For example, there is no deterioration of the quality of the cooked product, particularly due to changes in the cooking times, without the user having to implement a manual intervention in the cooking device, particularly at component parts of the gas feed or of the air feed, for adaptation to the environmental conditions, in that an automatic regulation of the air/combustion gas composition is implemented for setting a specific air ratio. The setting of a complete and, thus, hygienic combustion having a prescribed calorific output is thereby accomplished exclusively via changes of the gas feed, whereas the air quantity is held constant for a prescribed calorific output and, thus, the air ratio is set only via the variation of the supplied quantity of gas. Over and above this, the recognition of the momentary combustion condition is inventively possible by an indirect recognition of the caloric value, in that the linear relationship between the calorific value and the air requirement forms the basis. What the method also achieves is that additional inserts in the cooking device are avoided, the operating costs are not increased and a higher operating dependability is assured.
Other advantages and features of the invention will be readily apparent from the following description, the claims and drawings.